Reason may not be the only way of finding the truth, but it is a way on which we often rely. “The subway ran yesterday at 6:00 A.M. and the day before at 6:00 A.M. and the day before that, so I infer from this evidence that it will also run today at 6:00 A.M.” (a form of reasoning known as induction). “Bus drivers require would-be passengers to present the exact change; I don’t have the exact change; therefore, I infer I cannot ride on the bus” (deduction). (The terms deduction and induction are discussed in more detail on in Some Procedures in Argument.)

We also know that if we set our minds to a problem, we can often find reasons (not always necessarily sound ones) for almost anything we want to justify. Here’s an entertaining example from Benjamin Franklin’s Autobiography:

I believe I have omitted mentioning that in my first voyage from Boston, being becalmed off Block Island, our people set about catching cod and hauled up a great many. Hitherto I had stuck to my resolution of not eating animal food, and on this occasion, I considered with my master Tryon the taking of every fish as a kind of unprovoked murder, since none of them had or ever could do us any injury that might justify the slaughter. All this seemed very reasonable. But I had formerly been a great lover of fish, and when this came hot out of the frying pan, it smelt admirably well. I balanced some time between principle and inclination, till I recollected that when the fish were opened I saw smaller fish taken out of their stomachs. Then thought I, if you eat one another, I don’t see why we mayn’t eat you. So I dined upon cod very heartily and continued to eat with other people, returning only now and then occasionally to a vegetable diet. So convenient a thing it is to be a reasonable creature, since it enables one to find or make a reason for everything one has a mind to do.

Franklin is being playful; he is not engaging in critical thinking. He tells us that he loved fish and that this fish “smelt admirably well,” so we’re prepared for him to find a reason (here one as weak as “Fish eat fish, therefore people may eat fish”) to abandon his vegetarianism. (But think: Fish also eat their own young. May we therefore eat ours?)

Still, Franklin touches on a truth: If necessary, we can find reasons to justify whatever we want. That is, instead of reasoning, we may rationalize (devise a self-serving but dishonest reason), like the fox in Aesop’s fables who, finding the grapes he desired were out of reach, consoled himself with the thought that they were probably sour.

Perhaps we can never be certain that we aren’t rationalizing, except when being playful like Franklin. But we can seek to think critically about our own beliefs, scrutinizing our assumptions, looking for counterevidence, and wondering if it’s reasonably possible to draw different conclusions.